Airbags have continued to be installed in motor vehicles for the purpose of reducing the impact on the human body during a collision accident involving a vehicle such as an automobile. At the time of impact, the airbag is inflated by a gas to deploy in the form of a bag that absorbs and reduces impact on the body, and in addition to airbags for the driver's seat and front passenger seat, various types of airbags such as curtain airbags, side airbags, knee airbags or rear airbags are also being applied practically to protect occupants. Moreover, airbags have also been proposed for use as airbags installed so as to inflate outside of a vehicle in order to protect pedestrians.
Airbags such as curtain airbags, which deploy and inflate from the ceiling of the vehicle above the doors to protect the head during a side collision, or side impact airbags, which deploy and inflate from the passenger seats in order to protect the chest and lower back regions, are required to deploy rapidly and protect the body due to the short distance between the sidewall of the vehicle and the body.
When not in use, these airbags are stored by being folded into a compact form. When a collision is detected by a sensor and the airbag is deployed and inflated, the airbag flies out into the cabin by breaking through the fittings of ceiling trim covers or sewn parts of passenger seats while being unfolded by gas generated by an inflator, thereby enabling the airbag to absorb impacts and protect the body when fully inflated.
It is necessary to enhance pressure resistance of the bag body in order to make airbags requiring rapid deployment to demonstrate a higher degree of safety. In order to accomplish this, it is necessary not only to enhance the strength of the airbag base fabric but also the sewn parts where breaking strength is weak.
Various proposals have previously been made for modifying and improving the properties of the sewn parts of airbags.
For example, in Patent Document 1 indicated below, lock stitching is carried out using sewing thread having high rupture elongation, and seam slippage observed after deployment are inhibited to the degree of chain stitching despite being lock stitched. However, sewing thread having high elongation is disadvantageous for rapid deployment while preventing gas leakage and without causing a decrease in gas utilization efficiency during high pressure deployment. In addition, technology has yet to be disclosed regarding the properties of airbag base fabric as related to the strength of sewn parts.
In addition, in Patent Document 2 indicated below, sewing thread composed of aramid fibers is used to sew around the mouth for mounting an inflator. Although the use of heat-resistant, ultra-high-strength thread for the sewing thread in the vicinity of an inflator is useful, technology has yet to be disclosed regarding the properties of airbag base fabric as related to the strength of sewn parts.
Patent Document 3 indicated below indicates that the gas injection pressure resistance of an airbag is enhanced by increasing the pullout resistance of the composite yarns of the base fabric. Consequently, Patent Document 3 discloses sewing a high-density woven fabric having a cover factor of 1700 or more and air permeability of 1.5 cc/cm2/sec or less using sewing thread having a specific fineness under specific sewing conditions. Although the woven fabric has high density, is resistant to the formation of openings therein, has high pullout resistance and high airbag pressure resistance, it was inadequate in terms of enhancing stitch strength and high-pressure deployment at high speeds.
Patent Document 4 indicated below discloses sewing thread having tensile strength of 9 cN/dtex or more as well as high loop strength. Although gas infusion pressure resistance of an airbag is enhanced by enhancing the properties of the sewing thread, technology is not disclosed regarding properties of the airbag base fabric as related to the strength of sewn parts.
Moreover, technology has yet to be disclosed relating to an airbag that demonstrates high stitch strength even after having been exposed to a high-temperature environment, demonstrates high pressure resistance during high-pressure deployment at high speeds, and demonstrates a higher degree of safety.